1. Field of the Invention:
The present invention relates to a display device which displays by impressing drive signals on pixel electrodes used for display through switching elements, and more particularly to a display device which can perform a high density display by arranging pixel electrodes in a matrix.
2. Description of the Prior Art:
A liquid crystal display device, an EL display device and a plasma display device are known in the art in which pixel electrodes are selected and driven so as to display desired patterns on a screen. The display medium sealed between the electrodes is optically modulated by impressing a voltage between the selected pixel electrodes and the respective counter electrodes. The optical modulation is visually observed. An active matrix driving method is known as a driving method of pixel electrode. The active matrix driving method will be described as follows:
Pixel electrodes are independently arranged, and then provided with switching elements. The pixel electrodes are driven through the switching elements. TFTs (thin film transistor), MIMs (metal-insulating layer-metal), MOS transistors, diodes, varistors and other known devices are known as switching elements which select and drive the pixel electrodes. This type of active matrix method enables the display device to have a good contrast in the picture, and finds many applications such as in television, word processors, and display panels of computer terminals.
In the known active matrix display devices, buses are likely to be formed with the possibility of breakage during the fabrication of switching elements, buses, pixel electrodes on the active matrix substrate. A possible breakage of buses is detected as a line defect on the screen. The line defect is fatal for the display device. Defective display devices must be discarded, thereby decreasing production yield of display devices.
In order to solve these problems mentioned above, various proposals have been made. One example is shown in FIG. 6. FIG. 6 shows an active matrix display which is driven by TFTs 31. The active matrix has a structure made by two layers in which a conductive film wiring 23 is stacked on source buses 22 which cross over gate buses 21. This active matrix has a dual structure which includes conductive film wiring 23 arranged on the source buses 22. This dual structure is obtained by leaving the transparent conductive film on the source buses 22 after the source buses 22 are formed in pattern, when pixel electrodes 41 are formed with a transparent conductive film.
However, in the dual structure described above, the source buses 22 and the conductive film wirings 23 pass portions stepped by the gate buses at the junctions of the gate buses 21 and the source buses 22, so that the source buses 22 and a conductive film wiring 23 are likely to break. This is caused by the fact that the source buses 22 and the conductive film wiring 23 do not fully cover the stepped portions made by the gate buses 21, and that the source buses 22 and the conductive film wiring 23 are separated owing to poor adhesion of the insulating films to the source buses 22. The problem of breakage is nevertheless not solved by the dual structure.
In addition, when the source buses 22 are fabricated by etching, the etchant is likely to erode the metal parts of the source buses 22. The source buses 22 are liable to breakage.